Thermal Conductive Sheet and Method for Producing the Same

Abstract

To provide a heat conductive sheet capable of favorably conducting heat in the thickness direction while having sufficient thickness accuracy.SOLUTION: There is provided a heat conductive sheet which contains a resin and a granular filler and is obtained by laminating a plurality of primary sheets containing a resin and a granular filler in the thickness direction, or by slicing a block body folded or rolled up at an angle of 45 degrees or less to the laminating direction, wherein the thermal conductivity in the thickness direction is 12 W / m K or more and the standard deviation of the thickness is 7.0 μm or less.SELECTED DRAWING: None

Description

Technical Field

[0001] The present invention relates to a heat conduction sheet and a method for manufacturing the heat conduction sheet.

Background Art

[0002] In recent years, electronic components such as plasma display panels (PDPs) and integrated circuit (IC) chips have been generating increasing amounts of heat as their performance improves. As a result, in electronic devices using such electronic components, it has become necessary to take measures to prevent functional failures due to temperature rises in the electronic components.

[0003] As a measure to prevent functional failures due to temperature rises in electronic components, generally, a method of promoting heat dissipation by attaching a heat dissipation body such as a metal heat sink, a heat radiation plate, or heat radiation fins to a heat generating body such as an electronic component is adopted. When using a heat dissipation body, a sheet-like member having thermal conductivity (heat conduction sheet) is used to efficiently transfer heat from the heat generating body to the heat dissipation body. For example, a heat conduction sheet containing a resin and particulate fillers is sandwiched between the heat generating body and the heat dissipation body, and the heat generating body and the heat dissipation body are brought into close contact with each other through this heat conduction sheet to transfer heat from the heat generating body to the heat dissipation body. Conventionally, attempts have been made to improve various properties of the heat conduction sheet (see, for example, Patent Document 1).

[0004] Patent Document 1 discloses a method of obtaining a heat conduction sheet by slicing a laminate obtained by laminating a primary sheet containing a resin and a particulate carbon material in the thickness direction at an angle of 45° or less with respect to the lamination direction and then pressing the sheet obtained by the slicing. According to Patent Document 1, the heat conduction sheet obtained by the above-described method can exhibit excellent thermal conductivity even when used at a relatively low clamping pressure.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] Here, in recent years, from the viewpoint of making the heat generating body and the heat radiating body adhere well through the heat conductive sheet and uniformly transferring heat from the heat generating body to the heat radiating body, it has been required to improve the thickness accuracy of the heat conductive sheet. However, with the above conventional method, it has been difficult to produce a heat conductive sheet having a uniform thickness and to make the heat conductive sheet exhibit excellent heat conductivity in the thickness direction.

[0007] Therefore, an object of the present invention is to provide a heat conductive sheet capable of satisfactorily transferring heat in the thickness direction while having sufficient thickness accuracy, and a method for manufacturing the heat conductive sheet.

Means for Solving the Problems

[0008] The present inventor has intensively studied to achieve the above object. First, the present inventors tried to improve the thickness accuracy of the heat conductive sheet by pressurizing after slicing described in Patent Document 1 above. However, according to the study by the present inventors, it is presumed that when the sliced sheet is strongly pressurized, it becomes difficult for the particulate filler to be oriented in the thickness direction in the obtained heat conductive sheet, but it has become clear that it is difficult to sufficiently ensure the efficiency of heat transfer per unit thickness (that is, the thermal conductivity in the thickness direction). Then, the present inventor found that in a heat conductive sheet containing a resin and a particulate filler, if the standard deviation of the thickness is set to a predetermined value or less and the thermal conductivity in the thickness direction is set to a predetermined value or more, a heat conductive sheet capable of satisfactorily transferring heat in the thickness direction while having sufficient thickness accuracy can be obtained, and completed the present invention.

[0009] That is, the object of the present invention is to advantageously solve the above problems. The heat conduction sheet of the present invention contains a resin and a particulate filler, has a thermal conductivity in the thickness direction of 12 W / m·K or more, and a standard deviation of the thickness of 7.0 μm or less. Thus, a heat conduction sheet containing a resin and a particulate filler, having a thermal conductivity in the thickness direction of the above value or more and a standard deviation of the thickness of the above value or less, has sufficient thickness accuracy and can transfer heat well in the thickness direction. In the present invention, the "thermal conductivity in the thickness direction" can be calculated using the method described in the examples of this specification. Also, in the present invention, the "standard deviation of the thickness" is a value obtained by measuring the thickness at any five points of the heat conduction sheet, and can be calculated, for example, using the method described in the examples of this specification.

[0010] Here, in the heat conduction sheet of the present invention, it is preferable that the content ratio of the particulate filler is 45% by volume or less. If the volume ratio of the particulate filler in the heat conduction sheet is the above value or less, the thickness accuracy can be further improved while ensuring the flexibility of the heat conduction sheet.

[0011] And the heat conduction sheet of the present invention can have a main surface area of 30 cm 2 or more. In the present invention, the "main surface" refers to the surface having the largest area in the heat conduction sheet or the like.

[0012] Also, in the heat conduction sheet of the present invention, it is preferable that the average thickness is 200 μm or less. If the average thickness of the heat conduction sheet is the above value or less, heat can be transferred more favorably in the thickness direction of the heat conduction sheet. In the present invention, the "average thickness" is a value obtained by measuring the thickness at any five points of the heat conduction sheet, and can be calculated, for example, using the method described in the examples of this specification.

[0013] Furthermore, it is preferable that the surface roughness Sa of at least one main surface of the heat conduction sheet of the present invention is 2.80 μm or less. If the surface roughness Sa of at least one main surface is equal to or less than the above value, heat can be transferred more favorably in the thickness direction of the heat conduction sheet. In the present invention, the "surface roughness Sa" is a value obtained in accordance with the international standard ISO 25178 and can be measured, for example, using the method described in the examples of this specification.

[0014] Also, this invention aims to advantageously solve the above problems. The manufacturing method of the heat conduction sheet of the present invention includes a step of slicing a block body containing a resin and a particulate filler and having an Asker C hardness of 35 or more and 90 or less, using a blade with a tip curvature radius R of 1.0 μm or more and 12.0 μm or less. In this way, by slicing a block body containing a resin and a particulate filler and having an Asker C hardness within the above range, using a blade with a tip curvature radius R within the above range, a heat conduction sheet having sufficient thickness accuracy and capable of transferring heat favorably in the thickness direction can be obtained. In the present invention, the "Asker C hardness" is a value measured at a temperature of 25°C using a hardness tester in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS) and can be measured, for example, using the method described in the examples of this specification. In the present invention, the "tip curvature radius R" can be measured using the method described in the examples of this specification.

[0015] Here, in the manufacturing method of the heat conduction sheet of the present invention, in the slicing step, it is preferable that the slice width is 210 μm or less. If the block body is sliced with a slice width equal to or less than the above value, the thickness of the heat conduction sheet can be reduced, and heat can be transferred more favorably in the thickness direction of the heat conduction sheet. In the present invention, the "slice width" means the average value of the distance by which the block body and the blade relatively move in the above-mentioned fixed direction from the nth (n is a natural number of 1 or more) slice to the (n + 1)th slice when continuously slicing the block body while relatively moving the block body and the blade in a fixed direction to manufacture a plurality of heat conduction sheets.

[0016] And the method for manufacturing a heat conduction sheet of the present invention may further include a step of obtaining the block body by laminating a plurality of primary sheets containing a resin and a particulate filler in the thickness direction, or by folding or winding the primary sheet, prior to the slicing step. In this specification, "lamination", "folding", or "winding" may sometimes be collectively abbreviated as "lamination etc.".

[0017] Also, in the method for manufacturing a heat conduction sheet of the present invention, it is preferable that the tensile strength of the primary sheet is 0.3 MPa or more and 1.9 MPa or less. If the tensile strength of the primary sheet is within the above range, the thickness accuracy of the heat conduction sheet can be further improved. In the present invention, the tensile strength is a value obtained in accordance with JIS K6251, and can be measured, for example, using the method described in the examples of this specification.

Advantages of the Invention

[0018] According to the present invention, it is possible to provide a heat conduction sheet capable of satisfactorily transferring heat in the thickness direction while having sufficient thickness accuracy, and a method for manufacturing the heat conduction sheet.

Brief Description of the Drawings

[0019]

Figure 1

Embodiments for Carrying Out the Invention

[0020] Hereinafter, embodiments of the present invention will be described in detail. The heat conduction sheet of the present invention can be used, for example, by being sandwiched between a heating element and a heat radiator when attaching the heat radiator to the heating element. That is, the heat conduction sheet of the present invention can constitute a heat dissipation device together with a heat radiator such as a heat sink, a heat dissipation plate, and heat dissipation fins. And the heat conduction sheet of the present invention can be manufactured, for example, according to the manufacturing method of the heat conduction sheet of the present invention.

[0021] (Heat conduction sheet) The heat conduction sheet of the present invention contains a resin and a particulate filler, and may optionally further contain an additive. Also, the heat conduction sheet of the present invention has a thermal conductivity in the thickness direction of 12 W / m·K or more and a standard deviation of the thickness of 7.0 μm or less. And since the heat conduction sheet of the present invention has a thermal conductivity in the thickness direction of 12 W / m·K or more and a standard deviation of the thickness of 7.0 μm or less, it can transfer heat well in the thickness direction while having sufficient thickness accuracy.

[0022] <Resin> The resin contained in the heat conduction sheet is not particularly limited, and any resin can be used. For example, as the resin, both a liquid resin and a solid resin can be used. Note that the resin may be used alone or in combination of two or more. For example, the heat conduction sheet can contain at least one of a liquid resin and a solid resin, but from the viewpoint of further improving the thickness accuracy of the heat conduction sheet and transferring heat better in the thickness direction, it is preferable that the heat conduction sheet contains both a liquid resin and a solid resin.

[0023] <<Liquid resin>> And as the liquid resin, as long as it is liquid under normal temperature and pressure, it is not particularly limited, and for example, a thermoplastic resin that is liquid under normal temperature and pressure can be used. In the present invention, "normal temperature" refers to 23°C, and "normal pressure" refers to 1 atm (absolute pressure).

[0024] Examples of the liquid resin include a fluororesin, a silicone resin, an acrylic resin, and an epoxy resin. These may be used alone or in combination of two or more. Among them, as the liquid resin, a silicone resin and a fluororesin are preferable, and a fluororesin is more preferable. If at least one of a silicone resin and a fluororesin is used as the liquid resin, the flame retardancy of the heat conductive sheet can be improved. Further, if a fluororesin is used as the liquid resin, the heat resistance, oil resistance, and chemical resistance of the obtained heat conductive sheet can be improved.

[0025] [[Solid resin]] The solid resin is not particularly limited as long as it is not liquid under normal temperature and pressure. For example, a thermoplastic resin that is solid under normal temperature and pressure and a thermosetting resin that is solid under normal temperature and pressure can be used.

[0026] [Thermoplastic resin that is solid under normal temperature and pressure] Examples of thermoplastic resins that are solid under normal temperature and pressure include acrylic resins such as poly(2-ethylhexyl acrylate), copolymers of acrylic acid and 2-ethylhexyl acrylate, polymethacrylic acid or its esters, polyacrylic acid or its esters; silicone resins; fluorine resins; polyethylene; polypropylene; ethylene-propylene copolymers; polymethylpentene; polyvinyl chloride; polyvinylidene chloride; polyvinyl acetate; ethylene-vinyl acetate copolymers; polyvinyl alcohol; polyacetal; polyethylene terephthalate; polybutylene terephthalate; polyethylene naphthalate; polystyrene; polyacrylonitrile; styrene-acrylonitrile copolymers; acrylonitrile-butadiene copolymers (nitrile rubber); acrylonitrile-butadiene-styrene copolymers (ABS resin); styrene-butadiene block copolymers or their hydrogenated products; styrene-isoprene block copolymers or their hydrogenated products; polyphenylene ether; modified polyphenylene ether; aliphatic polyamides; aromatic polyamides; polyamide-imide; polycarbonate; polyphenylene sulfide; polysulfone; polyethersulfone; polyether nitrile; polyether ketone; polyketone; polyurethane; liquid crystal polymer; ionomer; etc. These may be used alone or in combination of two or more. In the present invention, rubber is included in "resin".

[0027] [Thermosetting resins that are solid under normal temperature and pressure] Examples of thermosetting resins that are solid at normal temperature and pressure include, for example, natural rubber; butadiene rubber; isoprene rubber; nitrile rubber; hydrogenated nitrile rubber; chloroprene rubber; ethylene propylene rubber; chlorinated polyethylene; chlorosulfonated polyethylene; butyl rubber; halogenated butyl rubber; polyisobutylene rubber; epoxy resin; polyimide resin; bismaleimide resin; benzocyclobutene resin; phenol resin; unsaturated polyester; diallyl phthalate resin; polyimide silicone resin; polyurethane; thermosetting polyphenylene ether; thermosetting modified polyphenylene ether; and the like. These may be used alone or in combination of two or more.

[0028] <<Content ratio of resin>> The content ratio of the resin in the heat conduction sheet is not particularly limited, but it is preferably 35% by mass or more, more preferably 45% by mass or more, still more preferably 55% by mass or more, preferably 95% by mass or less, more preferably 85% by mass or less, and still more preferably 75% by mass or less. If the content ratio of the resin is 35% by mass or more, the flexibility of the heat conduction sheet can be ensured while further improving the thickness accuracy of the heat conduction sheet. On the other hand, if the content ratio of the resin is 95% by mass or less, heat can be transferred better in the thickness direction of the heat conduction sheet.

[0029] <<Content ratio of liquid resin>> Also, the content ratio of the liquid resin in the resin (in other words, the ratio of the liquid resin in the total of the solid resin and the liquid resin) is not particularly limited, but it is preferably 30% by mass or more, more preferably 40% by mass or more, still more preferably 50% by mass or more, particularly preferably 60% by mass or more, preferably 95% by mass or less, more preferably 90% by mass or less, still more preferably 85% by mass or less, and particularly preferably 80% by mass or less. If the content ratio of the liquid resin in the resin is 30% by mass or more, the flexibility of the heat conductive sheet can be ensured while further improving the thickness accuracy. On the other hand, if the content ratio of the solid resin in the resin is 95% by mass or less, the thickness accuracy of the heat conductive sheet can be further improved.

[0030] <Particulate filler> The particulate filler contained in the heat conductive sheet is not particularly limited as long as it can impart thermal conductivity to the heat conductive sheet. And as such a particulate filler, a particulate carbon material having high thermal conductivity can be preferably used. Note that the particulate filler may be used alone or in combination of two or more.

[0031] <<Particulate carbon material>> The particulate carbon material is not particularly limited, and for example, graphite such as artificial graphite, flaky graphite, exfoliated graphite, natural graphite, acid-treated graphite, expandable graphite, expanded graphite; carbon black; etc. can be used. These may be used alone or in combination of two or more.

[0032] Among those described above, as the particulate carbon material, it is preferable to use expanded graphite. By using expanded graphite, the thermal conductivity in the thickness direction of the thermal conductive sheet is increased, and heat can be transferred more favorably in the thickness direction of the thermal conductive sheet. Here, expanded graphite can be obtained, for example, by subjecting expandable graphite obtained by chemically treating graphite such as flake graphite with sulfuric acid or the like to heat treatment to expand it and then refining it. And examples of the expanded graphite include EC1500, EC1000, EC500, EC300, EC100, EC50 (all are trade names) manufactured by Ito Graphite Industry Co., Ltd.

[0033] <<Properties of Particulate Filler>> The particulate filler preferably has a volume average particle diameter of 30 μm or more, more preferably 50 μm or more, still more preferably 100 μm or more, particularly preferably 150 μm or more, preferably 500 μm or less, more preferably 400 μm or less, still more preferably 300 μm or less, and particularly preferably 230 μm or less. If the volume average particle diameter of the particulate filler is 30 μm or more, it is presumed that a favorable heat transfer path of the particulate filler can be formed in the thermal conductive sheet, and the thermal conductivity in the thickness direction of the thermal conductive sheet is increased. As a result, heat can be transferred more favorably in the thickness direction of the thermal conductive sheet. On the other hand, if the volume average particle diameter of the particulate filler is 500 μm or less, the thickness accuracy of the thermal conductive sheet can be further improved. In the present invention, the "volume average particle diameter" can be measured in accordance with JIS Z8825, and represents the particle diameter at which the cumulative volume calculated from the small-diameter side is 50% in the particle size distribution (volume basis) measured by the laser diffraction method.

[0034] Further, the particulate filler preferably has an aspect ratio (major axis / minor axis) greater than 1 and 10 or less, more preferably greater than 1 and 5 or less. If the aspect ratio of the particulate filler is greater than 1 and 10 or less, it is presumed that the particulate filler is likely to be well oriented in the thickness direction in the heat conduction sheet, and the heat conductivity in the thickness direction of the heat conduction sheet increases. As a result, heat can be transferred better in the thickness direction of the heat conduction sheet. In the present invention, the "aspect ratio" can be obtained by observing the particulate filler with an SEM (scanning electron microscope), measuring the maximum diameter (major axis) and the particle diameter (minor axis) in the direction orthogonal to the maximum diameter for any 50 particulate fillers, and calculating the average value of the ratio of the major axis to the minor axis (major axis / minor axis). Further, in the above, for example, when the particulate filler has a scale shape, the "major axis" refers to the length in the major axis direction of the main surface of the scale shape, and the "minor axis" refers to the length in the direction orthogonal to the major axis of the main surface.

[0035] <<Content ratio of particulate filler>> The content ratio of the particulate filler in the heat conduction sheet is not particularly limited, but is preferably 5% by volume or more, more preferably 10% by volume or more, still more preferably 20% by volume or more, preferably 45% by volume or less, more preferably 35% by volume or less, and still more preferably 30% by volume or less. If the content ratio of the particulate filler is 5% by volume or more, the heat conductivity in the thickness direction of the heat conduction sheet increases, and heat can be transferred better in the thickness direction of the heat conduction sheet. On the other hand, if the content ratio of the particulate filler is 45% by volume or less, the flexibility of the heat conduction sheet can be ensured while further improving the thickness accuracy.

[0036] In addition, the content ratio of the particulate filler in the heat conductive sheet is not particularly limited, but it is preferably 5% by mass or more, more preferably 15% by mass or more, still more preferably 25% by mass or more, preferably 70% by mass or less, more preferably 55% by mass or less, and still more preferably 45% by mass or less. If the content ratio of the particulate filler is 5% by mass or more, the thermal conductivity in the thickness direction of the heat conductive sheet increases, and heat can be transferred more favorably in the thickness direction of the heat conductive sheet. On the other hand, if the content ratio of the particulate filler is 70% by mass or less, the flexibility of the heat conductive sheet can be ensured while further improving the thickness accuracy of the heat conductive sheet.

[0037] In addition, the content of the particulate filler in the heat conductive sheet is not particularly limited, but it is preferably 20 parts by mass or more, more preferably 30 parts by mass or more, still more preferably 40 parts by mass or more, preferably 100 parts by mass or less, more preferably 80 parts by mass or less, and still more preferably 60 parts by mass or less per 100 parts by mass of the resin. If the content of the particulate filler is 20 parts by mass or more per 100 parts by mass of the resin, the thermal conductivity in the thickness direction of the heat conductive sheet increases, and heat can be transferred more favorably in the thickness direction of the heat conductive sheet. On the other hand, if the content of the particulate filler is 100 parts by mass or less per 100 parts by mass of the resin, the flexibility of the heat conductive sheet can be ensured while further improving the thickness accuracy of the heat conductive sheet.

[0038] <Additive> In the heat conduction sheet of the present invention, known additives that can be used for forming the heat conduction sheet can be further blended as necessary. And the additives that can be blended in the heat conduction sheet are not particularly limited. For example, plasticizers such as fatty acid esters such as sebacic acid ester; flame retardants such as red phosphorus-based flame retardants and phosphate ester-based flame retardants; toughness improvers such as urethane acrylate; moisture absorbents such as calcium oxide and magnesium oxide; adhesion improvers such as silane coupling agents, titanium coupling agents, and acid anhydrides; wettability improvers such as nonionic surfactants and fluorine-based surfactants; ion trappers such as inorganic ion exchangers; and the like. Note that the additives may be used alone or in combination of two or more.

[0039] And when the heat conduction sheet further contains an additive, the blending amount of the additive can be, for example, 0.1 part by mass or more and 20 parts by mass or less, preferably 10 parts by mass or less, based on 100 parts by mass of the resin described above.

[0040] <Properties of the heat conduction sheet> The heat conduction sheet needs to have a thermal conductivity in the thickness direction of 12 W / m·K or more, more preferably 13 W / m·K or more, and still more preferably 14 W / m·K or more. If the thermal conductivity of the heat conduction sheet in the thickness direction is less than 12 W / m·K, heat cannot be transferred well in the thickness direction of the heat conduction sheet. And the upper limit of the value of the thermal conductivity of the heat conduction sheet in the thickness direction is not particularly limited, but is, for example, 50 W / m·K or less. Note that the thermal conductivity of the heat conduction sheet in the thickness direction can be adjusted by changing the types and content ratios of the materials (resins, particulate fillers, etc.) used in the production of the heat conduction sheet, as well as the production conditions of the heat conduction sheet. For example, by changing the volume average particle diameter and / or the content ratio of the particulate filler in the heat conduction sheet, the thermal conductivity of the heat conduction sheet in the thickness direction can be increased. Also, for example, by producing the heat conduction sheet using the production method of the heat conduction sheet of the present invention described later, the thermal conductivity of the heat conduction sheet in the thickness direction can be increased.

[0041] In addition, the thermal conductive sheet needs to have a standard deviation of thickness of 7.0 μm or less, preferably 6.0 μm or less, more preferably 5.0 μm or less, and still more preferably 4.0 μm or less. If the standard deviation of thickness exceeds 7.0 μm, the thickness accuracy of the thermal conductive sheet will be impaired. Therefore, it becomes difficult to make the heat generating body and the heat radiating body adhere well through the thermal conductive sheet, and heat transfer from the heat generating body to the heat radiating body cannot be performed uniformly. And the lower limit of the value of the standard deviation of the thickness of the thermal conductive sheet is not particularly limited, but is, for example, 1.0 μm or more. Incidentally, the standard deviation of the thickness of the thermal conductive sheet can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used in the production of the thermal conductive sheet, as well as the production conditions of the thermal conductive sheet. For example, by manufacturing the thermal conductive sheet using the manufacturing method of the thermal conductive sheet of the present invention described later, the standard deviation of the thickness of the thermal conductive sheet can be increased. More specifically, in the manufacturing method of the thermal conductive sheet of the present invention, by changing the tensile strength of the primary sheet, the Asker C hardness of the block body, and / or the radius of curvature R of the tip of the blade used for slicing, the standard deviation of the thickness of the thermal conductive sheet can be decreased.

[0042] In addition, the thermal conductive sheet preferably has an average thickness of 70 μm or more, more preferably 80 μm or more, preferably 200 μm or less, more preferably 160 μm or less, still more preferably 130 μm or less, and particularly preferably 110 μm or less. If the average thickness is 70 μm or more, the strength of the thermal conductive sheet can be ensured, and if it is 200 μm or less, heat transfer can be performed better in the thickness direction of the thermal conductive sheet.

[0043] In addition, the thermal conductive sheet can have a main surface area of, for example, 30 cm 2 or more, 50 cm 2 or more, 80 cm 2 or more, 100 cm 2 or more, 1000 cm 2The following can be adopted.

[0044] And, it is preferable that the surface roughness Sa of at least one main surface of the heat conductive sheet is 2.80 μm or less, more preferably 2.60 μm or less, still more preferably 2.20 μm or less, and particularly preferably 2.00 μm or less. If the surface roughness Sa of the main surface is 2.80 μm or less, since the main surface is sufficiently smooth, when the heat conductive sheet is sandwiched between the heat generating body and the heat radiating body and used, the heat conductive sheet and the heat generating body and / or the heat radiating body are in good contact, and the interfacial resistance is reduced. Therefore, heat can be transferred more favorably in the thickness direction of the heat conductive sheet. And, the lower limit of the value of the surface roughness Sa of the main surface of the heat conductive sheet is not particularly limited, but is, for example, 1.00 μm or more. Furthermore, from the viewpoint of more favorably transferring heat in the thickness direction of the heat conductive sheet, it is preferable that the surface roughness Sa of both main surfaces (front surface and back surface) of the heat conductive sheet is below the above-described preferable upper limit value. Note that the surface roughness Sa of the main surface of the thickness of the heat conductive sheet can be adjusted by changing the type and content ratio of the material (resin, particulate filler, etc.) used in the production of the heat conductive sheet, as well as the production conditions of the heat conductive sheet. For example, by manufacturing the heat conductive sheet using the manufacturing method of the heat conductive sheet of the present invention described later, the surface roughness Sa of the heat conductive sheet can be reduced. More specifically, in the manufacturing method of the heat conductive sheet of the present invention, the surface roughness Sa of the main surface of the heat conductive sheet can be reduced by changing the tensile strength of the primary sheet, the Asker C hardness of the block body, and / or the radius of curvature R of the tip of the blade used for slicing.

[0045] (Manufacturing method of heat conductive sheet) The heat conductive sheet of the present invention described above can be manufactured, for example, using the manufacturing method of the heat conductive sheet of the present invention. Here, the manufacturing method of the heat conductive sheet of the present invention includes at least a step (slicing step) of slicing a block body containing a resin and a particulate filler and having an Asker C hardness of 35 or more and 90 or less using a blade having a tip radius of curvature R of 1.0 μm or more and 12.0 μm or less. According to the method for manufacturing the heat conduction sheet of the present invention, a heat conduction sheet having sufficient thickness accuracy and capable of favorably conducting heat in the thickness direction can be obtained.

[0046] <Slicing step> In the slicing step, as described above, a block body having an Asker C hardness of 35 or more and 90 or less is sliced using a blade with a tip curvature radius R of 1.0 μm or more and 12.0 μm or less to cut out a heat conduction sheet from the block body.

[0047] [[Block body]] The block body contains a resin and a particulate filler, and may optionally further contain an additive. The block body has an Asker C hardness of 35 or more and 90 or less.

[0048] [Resin, particulate filler, and additive] The suitable types, properties, and content ratios of the resin, particulate filler, and optionally included additive contained in the block body can be the same as the suitable types, properties, and content ratios described above for the heat conduction sheet of the present invention.

[0049] [Asker C hardness] Here, it is necessary for the block body to have an Asker C hardness of 35 or more and 90 or less, preferably 85 or less, more preferably 80 or less, preferably 40 or more, more preferably 50 or more, and still more preferably 60 or more. When the Asker C hardness exceeds 90, it becomes difficult to sufficiently ensure the thickness accuracy of the heat conduction sheet obtained by slicing the block body (particularly the thickness accuracy when reducing the thickness of the heat conduction sheet by reducing the slice width). On the other hand, when the Asker C hardness is less than 35, blurring of the blade tip during slicing due to the adhesiveness of the block body or the like cannot be suppressed, and the thickness accuracy of the heat conduction sheet decreases. Note that the Asker C hardness of the block body can be adjusted by changing the types and content ratios of the materials (resin, particulate filler, etc.) used in the manufacture of the block body and the manufacturing method of the block body.

[0050] <<Blade>> The shape of the blade used for slicing the above-mentioned block body is not particularly limited, and it may be a single-edge blade, a double-edge blade, or an asymmetric blade. However, from the perspective of sufficiently ensuring the thickness accuracy of the obtained heat conduction sheet, a double-edge blade is preferred. Also, the material of the blade is not particularly limited, but it is preferably made of metal.

[0051] And, the blade used for slicing the block body needs to have a tip curvature radius R of 1.0 μm or more and 12.0 μm or less as described above. It is preferably 1.5 μm or more, more preferably 4.5 μm or more, preferably 10.0 μm or less, more preferably 9.0 μm or less, still more preferably 7.0 μm or less, and particularly preferably 5.0 μm or less. If the tip curvature radius R of the blade is less than 1.0 μm, the blade may bite during slicing, and there is a risk of reducing the manufacturing efficiency of the heat conduction sheet. On the other hand, if the tip curvature radius R of the blade exceeds 12.0 μm, it becomes difficult to ensure the thickness accuracy of the heat conduction sheet obtained by slicing the block body (particularly, the thickness accuracy when reducing the thickness of the heat conduction sheet by reducing the slice width), or it becomes difficult to slice because the blade with an obtuse angle does not bite into the block body.

[0052] <<Slice>> The method of slicing the block body is not particularly limited as long as it uses a blade with a tip curvature radius R within the above-mentioned range. And for slicing, a cutting tool equipped with a blade with a tip curvature radius R within the above-mentioned range can be used. Examples of such cutting tools include cutters, knives, and slicers.

[0053] Here, when the block body is a laminate obtained by laminating a primary sheet or the like by the laminating process described later, the angle at which the block body is sliced is preferably 45° or less with respect to the laminating direction, more preferably 30° or less with respect to the laminating direction, still more preferably 15° or less with respect to the laminating direction, and particularly preferably substantially 0° with respect to the laminating direction (i.e., the direction along the laminating direction). When the block body is a laminate obtained by laminating a primary sheet or the like, it is presumed that the particulate filler is oriented in a direction substantially orthogonal to the laminating direction inside the block body. And if such a block body is sliced at an angle of 45° or less with respect to the laminating direction, in the obtained heat conductive sheet, the particulate filler is oriented in the thickness direction (i.e., the direction substantially orthogonal to the laminating direction of the primary sheet), and it is presumed that the heat transfer path formed by the contact of the particulate filler is preferably formed well mainly in the thickness direction of the heat conductive sheet, so that heat can be transferred better in the thickness direction of the heat conductive sheet.

[0054] Also, from the viewpoint of easily slicing the block body and sufficiently ensuring the thickness accuracy of the obtained heat conductive sheet, the temperature of the block body during slicing is preferably -20°C or higher and 80°C or lower, and more preferably -10°C or higher and 50°C or lower. Furthermore, from the viewpoint of easily slicing the block body and sufficiently ensuring the thickness accuracy of the obtained heat conductive sheet, it is preferable to fix the block body by applying pressure or the like during slicing. In such pressing, the surface to which pressure is applied is not particularly limited.

[0055] <Other Processes> The other processes that the manufacturing method of the heat conductive sheet of the present invention may optionally include are not particularly limited. For example, in the manufacturing method of the heat conductive sheet of the present invention, before the slicing process described above, a step (laminating step) of laminating a plurality of primary sheets containing a resin and a particulate filler in the thickness direction, or folding or winding this primary sheet to obtain a block body can be carried out. Also, in the method for manufacturing the heat conduction sheet of the present invention, before the slicing step described above, a step of heating the block body (heating step) can be carried out. In the method for manufacturing the heat conduction sheet of the present invention, as long as the effects of the present invention are not significantly impaired, a step of pressing the heat conduction sheet obtained after the slicing step in the thickness direction (pressing step) may be carried out. However, from the viewpoint of suppressing a decrease in the thermal conductivity in the thickness direction of the obtained heat conduction sheet, the method for manufacturing the heat conduction sheet of the present invention preferably does not include the pressing step. Hereinafter, the lamination step and the heating step as other steps will be described in detail.

[0056] <<Lamination Step>> As described above, in the lamination step, a plurality of primary sheets are laminated in the thickness direction, or the primary sheet is folded or wound to obtain a block body which is a laminate.

[0057] [Primary Sheet] The primary sheet contains a resin and a particulate filler, and may further optionally contain an additive.

[0058] - Resin, Particulate Filler, and Additive - The suitable types, properties, and content ratios of the resin, particulate filler, and optionally included additive contained in the primary sheet can be the same as the suitable types, properties, and content ratios of the respective components described above for the block body and the heat conduction sheet of the present invention.

[0059] - Properties of the Primary Sheet - The primary sheet preferably has a tensile strength of 0.3 MPa or more, more preferably 0.4 MPa or more, still more preferably 0.6 MPa or more, preferably 1.9 MPa or less, more preferably 1.6 MPa or less, and still more preferably 1.4 MPa or less. If the tensile strength is 0.3 MPa or more, the Asker C hardness of the block body obtained by laminating the primary sheets or the like increases. Therefore, it is possible to obtain a heat conductive sheet with even better thickness accuracy by suppressing the blade wobbling when slicing the block body. On the other hand, if the tensile strength is 1.9 MPa or less, the Asker C hardness of the block body obtained by laminating the primary sheets or the like does not increase excessively. Therefore, slicing of the block body becomes easy, and sufficient thickness accuracy (particularly, thickness accuracy when reducing the thickness of the heat conductive sheet by reducing the slice width) of the obtained heat conductive sheet can be ensured. Incidentally, the tensile strength of the primary sheet can be adjusted by changing the type and content ratio of the materials (resin, particulate filler, etc.) used in the production of the primary sheet and the production method of the primary sheet. For example, by increasing the resin content ratio in the primary sheet, the tensile strength of the primary sheet can be increased.

[0060] Also, the thickness (average thickness) of the primary sheet is not particularly limited, and can be, for example, 0.05 mm or more and 2 mm or less. Incidentally, the "thickness (average thickness)" of the primary sheet can be measured in the same manner as the "average thickness" of the heat conductive sheet.

[0061] - Preparation method of primary sheet - The preparation method of the primary sheet is not particularly limited. The primary sheet can be obtained, for example, by molding a composition containing a resin, a particulate filler, and optionally used additives by a known molding method such as press molding, rolling molding, or extrusion molding.

[0062] [Formation of block body by lamination etc.] The formation of the block body by laminating the primary sheets or the like is not particularly limited and may be performed using a laminating device or manually. Also, the formation of the block body by folding the heat conduction sheet is not particularly limited and can be performed by folding the primary sheet to a certain width using a folding machine. Further, the formation of the block body by winding the primary sheet can be performed by winding the primary sheet around an axis parallel to the short side direction or the long side direction of the primary sheet without particular limitation.

[0063] <<Heating Step>> Here, for example, the block body obtained through the above-described lamination step may be directly subjected to the slicing step, or may be subjected to the slicing step after further heating the block body. The heating temperature in the heating step can be, for example, 50°C or higher and 170°C or lower, and the heating time can be, for example, 1 minute or longer and 8 hours or shorter. By going through the heating step, the Asker C hardness of the block body can be adjusted. For example, when the block body contains a thermoplastic resin, the Asker C hardness of the block body can be decreased by performing the heating step.

Examples

[0064] Hereinafter, the present invention will be specifically described based on examples, but the present invention is not limited to these examples. In the following description, “%” and “parts” representing amounts are based on mass unless otherwise specified. In the examples and comparative examples, the radius of curvature R of the tip of the blade, the tensile strength of the primary sheet, the Asker C hardness of the block body, and the average thickness, standard deviation of the thickness, surface roughness Sa, thermal conductivity in the thickness direction, and thermal resistance value in the thickness direction of the heat conduction sheet were measured or evaluated according to the following methods, respectively.

[0065] <Radius of Curvature R> The radius of curvature R of the tip of the blade was measured using a full focus 3D surface shape measuring device (manufactured by Alicona imaging, product name “Infinite Focus G5”). Specifically, spot light was applied coaxially from the cutting edge direction, and the tip shape was measured using a 50x lens. Also, the blade was fixed with the entire blade tilted 20 degrees with respect to the spot light. Regarding the 3D image of the tip of the obtained blade, cross-sectional observation was performed at an arbitrary cross-section, an inner circle was drawn so that approximately half of the circumference touched the tip of the blade, and the radius thereof was defined as the radius of curvature R of the tip of the blade. <Tensile strength> The primary sheet was punched and formed into dumbbell No. 2 in accordance with JIS K6251 to prepare a sample piece. Using a tensile testing machine (manufactured by Shimadzu Corporation, product name "AG-IS20kN"), the portions 1 cm from both ends of the sample piece were pinched, and at a temperature of 23°C, in a direction perpendicular to the normal line emerging from the surface of the sample piece, the sample piece was pulled at a tensile speed of 500 mm / min, and the breaking strength (tensile strength) was measured. <Asker C hardness> The measurement of the Asker C hardness of the block body was carried out at a temperature of 25°C in accordance with the Asker C method of the Japan Rubber Association Standard (SRIS), using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ"). Specifically, the obtained laminate was left standing in a thermostatic chamber maintained at a temperature of 25°C for 48 hours or more to obtain a test body. Next, the hardness tester was installed so that the distance from the needle tip to the laminate surface was 2 cm, the damper was lowered, and the laminate and the damper were made to collide. The Asker C hardness of the laminate 60 seconds after the collision was measured twice using a hardness tester (manufactured by Kobunshi Keiki Co., Ltd., product name "ASKER CL-150LJ"), and the average value of the measurement results was adopted. <Average thickness> Using a thickness gauge (manufactured by Mitutoyo, product name "Digital Indicator ID-C112XBS"), the thicknesses at a total of five points, namely, the approximate center point and the four corners (squares) of the heat conduction sheet were measured, and the average value (μm) of the measured thicknesses was obtained. <Standard deviation of thickness> Using a thickness gauge (manufactured by Mitutoyo, product name "Digital Indicator ID-C112XBS"), the thicknesses at a total of five points, namely, the approximate center point and the four corners (squares) of the heat conduction sheet were measured, and the standard deviation (μm) of the measured thicknesses was obtained. <Surface roughness Sa> The surface roughness Sa of the heat conduction sheet was measured using a three-dimensional shape measuring machine (manufactured by Keyence Corporation, product name "One Shot 3D Measurement Macroscope"). Here, a heat conduction sheet cut into a substantially square shape of any size of 1 cm square or more was used as a sample, the analysis range was 1 cm × 1 cm, and the three-dimensional shapes of the front and back surfaces of the sample were measured respectively. Then, the surface roughness Sa (μm) was automatically calculated by further performing filter processing (2.5 mm) on the measurement results of the three-dimensional shape with software to remove the undulation component. <Thermal conductivity in the thickness direction> Regarding the heat conduction sheet, the thermal diffusivity α (m 2 / s), specific heat at constant pressure Cp (J / g·K), and specific gravity ρ (g / m 3 ) were measured by the following methods respectively. [Thermal diffusivity α in the thickness direction] It was measured based on the provisions of ISO 22007-3 using a thermal diffusivity and thermal conductivity measuring device (manufactured by Iphaze Corporation, product name "Iphaze Mobile 1u"). [Specific heat at constant pressure Cp] Using a differential scanning calorimeter (manufactured by Rigaku, product name "DSC8230"), the specific heat at 25°C was measured under the temperature rising condition of 10°C / min. [Specific gravity ρ (density)] It was measured using an automatic specific gravity meter (manufactured by Toyo Seiki Co., Ltd., product name "DENSIMETER-H"). Then, each measured value was substituted into the following formula (I): λ = α × Cp × ρ ··· (I) to obtain the thermal conductivity λ (W / m·K) in the thickness direction of the heat conduction sheet at 25°C. <Thermal resistance value> The thermal resistance value of the heat conduction sheet was measured using a thermal resistance tester (manufactured by Hitachi Technology and Services Co., Ltd., product name "Resin Material Thermal Resistance Measuring Device"). Here, a heat conduction sheet cut into a substantially square of 1 cm square was used as a sample, and the thermal resistance values (°C / W) when pressures of 0.1 MPa and 0.9 MPa were applied at a sample temperature of 50°C were measured. The smaller the thermal resistance value, the better the heat conductivity of the heat conduction sheet, for example, indicating excellent heat dissipation characteristics when interposed between a heating element and a heat sink.

[0066] (Example 1) <Formation of the primary sheet> 70 parts of a thermoplastic fluororesin that is liquid under normal temperature and pressure as a resin (manufactured by Daikin Industries, Ltd., product name "Dai-el G-101"), 30 parts of a thermoplastic fluororesin that is solid under normal temperature and pressure (manufactured by 3M Japan Ltd., product name "Dynion FC2211"), and 50 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., product name "EC100", volume average particle diameter: 200 μm) were stirred and mixed at a temperature of 150°C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the obtained mixture was put into a crusher (manufactured by Osaka Chemical Co., Ltd., product name "Wonder Crush Mill D3V-10") and crushed for 10 seconds. 50 g of the crushed mixture was sandwiched between polyethylene terephthalate (PET) films (protective films) with a thickness of 50 μm that had been subjected to sandblasting treatment, and rolled and formed under the conditions of a roll gap of 550 μm, a roll temperature of 50°C, a roll linear pressure of 50 kg / cm, and a roll speed of 1 m / min to obtain a primary sheet with a thickness of 0.8 mm. Then, the tensile strength of the primary sheet was measured. The results are shown in Table 1. <Lamination process> The obtained primary sheet was cut into a size of 150 mm in length × 150 mm in width × 0.8 mm in thickness, 100 sheets were laminated in the thickness direction of the primary sheet, and further pressed in the lamination direction at a temperature of 120°C and a pressure of 0.1 MPa for 3 minutes to obtain a block body (laminated body) with a height of about 80 mm. Then, the Asker C hardness of the obtained block body was measured. The results are shown in Table 1. <Slicing process> After that, leaving the necessary length for slicing, the entire upper surface of the obtained block body was pressed with a metal plate, and a pressure of 0.1 MPa was applied in the stacking direction (i.e., from above) to fix the block body. Note that the sides and the back of the block body were not fixed. At this time, the temperature of the block body was 25°C. Next, a blade 10 having the shape shown in FIG. 1 (double-edged, blade angle 2θ: 20°, maximum thickness of the blade part: 3.5 mm, material: super steel, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm, tip radius of curvature R: 1.7 μm) was attached to the press part of a servo press machine (manufactured by Discharge Precision Machining Laboratory), and the block body (laminated body) was sliced in the stacking direction (in other words, in the direction coinciding with the normal of the main surface of the laminated primary sheets) under the conditions of a slice width of 85 μm and a slice speed of 200 mm / second to obtain a heat conduction sheet having a main surface of 150 mm in length and 80 mm in width. Note that the posture of the blade during slicing was such that the angle α shown in FIG. 1 was 10°, and the extending direction of the blade surface 11 was parallel to the slice surface 21 of the block body 20. Then, the average thickness, standard deviation of the thickness, surface roughness Sa, thermal conductivity in the thickness direction, and thermal resistance value of the obtained heat conduction sheet were measured. The results are shown in Table 1.

[0067] (Example 2) In the slicing step, a primary sheet, a block body, and a heat conduction sheet were produced and various evaluations were performed in the same manner as in Example 1, except that a blade (double-edged, blade angle 2θ: 20°, maximum thickness of the blade part: 3.5 mm, material: super steel, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm) with a tip radius of curvature R of 4.7 μm was used. The results are shown in Table 1.

[0068] (Example 3) A primary sheet was formed in the same manner as in Example 1. Next, in the stacking step, after stacking and pressing the primary sheets in the same manner as in Example 1, the obtained laminated body was further heated at 100°C for 3 hours (heating step) and then allowed to cool at room temperature for 3 hours. The Asker C hardness of the block body after this heating and cooling was measured. The results are shown in Table 1. Then, except for using the block body after this heating and cooling, the slicing process was carried out in the same manner as in Example 1 to produce a heat conduction sheet and various evaluations were performed. The results are shown in Table 1.

[0069] (Example 4) When forming the primary sheet, except for using only 100 parts of a thermoplastic fluororesin (manufactured by Daikin Industries, Ltd., product name "Dai-el G-101") that is liquid under normal temperature and pressure as the resin, the primary sheet, block body, and heat conduction sheet were produced in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1.

[0070] (Example 5) In the slicing process, except for using a blade with a tip radius of curvature R of 4.7 μm (double-edged, blade angle 2θ: 20°, maximum thickness of the blade part: 3.5 mm, material: super steel, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm), the primary sheet, block body, and heat conduction sheet were produced in the same manner as in Example 3, and various evaluations were performed. The results are shown in Table 1.

[0071] (Example 6) In the slicing process, a blade with a tip radius of curvature R of 9.1 μm (double-edged, blade angle 2θ: 20°, maximum thickness of the blade part: 3.5 mm, material: super steel, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm) was used, and except for changing the slicing width to 90 μm, the primary sheet, block body, and heat conduction sheet were produced in the same manner as in Example 1, and various evaluations were performed. The results are shown in Table 1.

[0072] (Example 7) <Formation of the primary sheet> 45 parts of a thermoplastic fluororesin that is liquid at normal temperature and pressure (manufactured by Daikin Industries, Ltd., product name "Dai-el G-101"), 40 parts of a thermoplastic fluororesin that is solid at normal temperature and pressure (manufactured by 3M Japan Ltd., product name "Dyneon FC2211"), 85 parts of expanded graphite as a particulate filler (manufactured by Ito Graphite Industry Co., Ltd., product name "EC100", volume average particle diameter: 250 μm), and 5 parts of sebacic acid ester as a plasticizer (manufactured by Daihachi Chemical Industry Co., Ltd., product name "DOS") were stirred and mixed at a temperature of 150 °C for 20 minutes using a pressure kneader (manufactured by Nippon Spindle). Next, the obtained mixture was put into a crusher (manufactured by Osaka Chemical Co., Ltd., product name "Wonder Crush Mill D3V-10") and crushed for 10 seconds. 50 g of the crushed mixture was roll-formed under the same conditions as in Example 1 to obtain a primary sheet with a thickness of 0.8 mm. Then, the tensile strength of the primary sheet was measured. The results are shown in Table 1. <Lamination step> A block body was obtained in the same manner as in Example 1 except that the above-described primary sheet was used. Then, the Asker C hardness of the obtained block body was measured. The results are shown in Table 1. <Slicing step> Using the above-described block body and changing the slice width to 160 μm, a heat conduction sheet was produced and various evaluations were performed in the same manner as in Example 1. The results are shown in Table 1.

[0073] (Comparative Example 1) In the same manner as in Example 1, a primary sheet and a block body were produced. Then, in the slicing step, a blade with a tip radius of curvature R of 13.5 μm (double-edged, blade angle 2θ: 20°, maximum thickness of the blade part: 3.5 mm, material: super steel, Rockwell hardness: 91.5, no silicon processing on the blade surface, total length: 200 mm) was used, and an attempt was made to slice the block body under the same conditions as in Example 1 except that the slice width was changed to 150 μm. However, since the cutting edge of the blade was poor, slicing could not be performed and a heat conduction sheet could not be obtained.

[0074] (Comparative Example 2) In the same manner as in Example 4, a primary sheet was formed. Next, in the lamination step, after laminating and pressing the primary sheet in the same manner as in Example 4, the obtained laminate was further heated at 100 °C for 3 hours (heating step) and then allowed to cool at room temperature for 3 hours. The Asker C hardness of the block body after this heating and cooling was measured. The results are shown in Table 1. Then, except for using the block body after this heating and cooling, a slicing step was carried out in the same manner as in Example 4 to produce a heat conduction sheet and various evaluations were performed. The results are shown in Table 1.

[0075]

Table 1

[0076] From Table 1, it can be seen that the heat conduction sheets of Examples 1 to 7 have a small thermal conductivity in the thickness direction and a low thermal resistance value in the thickness direction, so they can transfer heat well in the thickness direction. Also, since the heat conduction sheets of Examples 1 to 7 have a small value of the standard deviation of the thickness, it can be seen that they are excellent in thickness accuracy. On the other hand, as described above, in Comparative Example 1, slicing could not be performed because the cutting edge of the blade was dull, and a heat conduction sheet could not be obtained. Also, from Table 1, it can be seen that the heat conduction sheet of Comparative Example 2 is inferior in thickness accuracy because the value of the standard deviation of the thickness is large.

Industrial Applicability

[0077] According to the present invention, it is possible to provide a heat conduction sheet capable of transferring heat well in the thickness direction while having sufficient thickness accuracy, and a method for manufacturing the heat conduction sheet.

Explanation of Symbols

[0078] 10 Blade 11 Blade Surface 20 Block Body 21 Slicing Surface 30 Heat Conduction Sheet

Claims

1. A heat-conductive sheet containing a thermoplastic resin that is solid at normal temperature and pressure and a particulate filler, wherein the particulate filler is oriented at an angle of 45° or more with respect to the main surface of the heat-conductive sheet, the thermal conductivity in the thickness direction is 12 W / m·K or more, the standard deviation of the thickness is 7.0 μm or less, and the surface roughness Sa of at least one main surface is 2.60 μm or less.

2. The heat-conductive sheet according to claim 1, wherein the content ratio of the particulate filler is 45% by volume or less.

3. The area of the main surface is 30 cm ２ or more, the heat conductive sheet according to claim 1 or 2.

4. The heat-conductive sheet according to any one of claims 1 to 3, wherein the average thickness is 200 μm or less.

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